Recording and reproduction of sound waves



April 2, 1929.

RECORDING AND REPRODUCTION OF SOUND WAYES Filed Nov. 10, 1927 ator Rec-01w Transmitter l i 2558; u

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Patented fApr. 2,1929 I UNITED STATES 1,701,261 PATENT OFFICE.

cnaanns n. race-ran, or- MILLBU'RN, new JERSEY, ASSIGNOR To AmEmoAn ramrnoma AND TELEGRAPH company, A CQRZE'ORATION or new YORK.

-'BEGORDING AND REPRODUCTION OF SOUND WAVES.

Application filed November 10, 1927. Serial No..232,451.

I M the needle and therecord. The principal object of this invention is to eliminate this noise or needle scratch? The advantage foundinthe attainment of this object, and various other advantages of the invention, will appear in the following description.

The apparatus and the methods of this invention are modifications of the apparatus and methods disclosed in my copending ap- 2 plication filed as of even date herewith and given Serial No. 232,450.

It has been found experimentally that most of the noise known as needle scratch occurs below a frequency of approximately 5,000

cycles. In general, the method employed by the applicant in accordance with the present invention for avoiding such noise consists of modulating a carrier wave with the voice or other signal to be recorded and reproduced,

as cutting the record with the carrier and a side-band, reproducing the carrier and sideband and demodulating at the reproducing end to restore the original signal.

The invention will be more clearly underto stood when the following detailed description of a desirable embodiment thereof, and the recording and reproduction methods involvedfis read with reference to the'accom-. panyin drawing. he drawing shows scheas matical y the apparatusand circuit arrange inents by which the applicants object is accomplished. Figure 1 of the drawing shows the recording end of'the system, while Fig. 2 shows the reproduction end.

With reference to the details of the draw- 7 ing, there is-transmitted from a transmitter or other signal source signals covering a frequency range of 100 to 5,000 cycles, for instance. These signals are passed throughan 5 ampli'fier'A, and into a modulator, where they oil carrier and any other undesirable frequencies described for the purpose of illustration, it is rier and the side-band may then be amplifiedin an amplifier A and by means ofany suitable record-cutting device the .record is cut with the. carrier and side-band. frequencies.

, At the reproduction end of the system anelectrical phonograph and reproducer sets up in the circuit the carrier and side-band frequencies at which the record was out. In the reproduction, however, there may be introduced the needle scratch frequencies, which, a stated above, lie for the most part below 5, 00 cycles. In order to eliminate these noise frequencies a filter F is introduced into the circuit, this filter passing only the frequencies from 5,000 cycles to, say 10,100 cycles. These carrier and side-band frequencies are then fed into a demodulator, and the original signal is restored. A filter F may be introduced, as indicated in the drawing, which passes only the frequencies from 100 to 5,000 cycles, thus eliminating the which may be present. The resultant waves may then be passed through an amplifier A and on to a loud speaking receiver.

While the invention has been specifically to be understood that its scope is not'limitedby such description but is defined in the appended claims.

What I claimed is 1. The method. of recording and reproducin'g sound waves which consists'in modulating a carrier wave with the original waves, recording the carrier and a side-band produ'ced by said modulation, reproducing the 7 carrier and the side-band, eliminating after b reproduction all frequencies outside the range of the carrier and the side-band, and demodulating the combined carrier and sideband to restore the original waves. l

2. The method of recording and reproduc- 5 ing sound waves varying in frequency over a band of approximately to 5,000 cycles ,per second which consists in modulating a carrier wave with the original waves to pro-- duce a side-band having a lowerlimit of apmg the carrier and said side-band, reproducing the carrier and the side-band, eliminating after reproduction all frequencies outside the range of the carrier and the sidehand, and demodulating the combined 'carrier and side-band to restore the original waves- 3: Inna system for recording and reproducin sound waves,'means for combining the 'orlgifialwaves with a carrier wave, means for recording-the carrier and a si e-band produced. by said combination, means for reproducing' the carrier and the side-band, means 1 for separatingthe carrier and the side-band frequencies from any other frequencies produced in. said reproducing means, and 'de- -modulati'ng means for restoring the original frequencies.

4. In a system for recording and reproducin sound waves varying in frequency over a and of approximately 100 to 5,000 cycles per second, means for converting the original sound waves into electrical waves, means for combining said electrical waves with a carrier wave to produce a side-band having a lower limit of ap roximately 5,000 cycles per second, means or recording the carrier and said side-hand, means for reproducing the carrier and the side-band frequencies, means for separating the carrier and the sideband frequencies from any other frequencies produced in said reproducing means, demodulatmg means for restoring the original frequencies, and means for reconverting the re-' 'sultant waves into sound.

' In testimony whereof, I have signed my name to this specification this 9th day of November, v 1927,

CHARLES H. FETTER. 

